An organic EL (Electro-Luminescent) device emits light with a DC voltage applied to a fluorescent organic compound. Light emitting apparatuses, display devices, etc. which have a matrix array of pixels each having this organic EL device are attracting attention as the next generation display devices.
This organic EL device is a current driven device that emits light with luminance which is proportional to the current flowing. An active matrix driven display device with such organic EL devices has pixels each provided with a drive transistor which is formed by a field effect transistor (thin film transistor) and controls the current value of the current supplied to the organic EL device.
A capacitor is connected between the gate and source of the drive transistor, and holds a voltage corresponding to the degree of gradation of image data externally supplied and written in the capacitor.
When a voltage is applied between the drain and source of the drive transistor, the drive transistor supplies the current to the organic EL device while controlling the current value with a gate-source voltage (hereinafter called “gate voltage”) Vgs which is the voltage held in the capacitor. The organic EL device emits light with the luminance corresponding to the amount of the current supplied, so that the active matrix driven display device displays an image.
As a system of writing a voltage in a capacitor, there is a voltage writing system which applies a designated voltage between the gate and source of the drive transistor according to the degree of gradation of an image. Such a configuration is disclosed in, for example, Unexamined Japanese Patent Application KOKAI Publication No. H08-330600.
According to the voltage writing system, the current value of the current that flows to the organic EL device varies according to a time-dependent variation of the characteristic of the drive transistor. Even when the same voltage is applied between the gate and source of the drive transistor, therefore, the current value of the current flowing to the organic EL device changes, degrading the display quality.
As a solution to this shortcoming, there is a display device which applies a voltage, acquired by adding a gradation voltage and an offset voltage, to a data line, sequentially changes the offset voltage for a predetermined unit voltage, compares the current flowing to a power supply line with a reference current to acquire variation of the characteristic of the drive transistor, and corrects the voltage value of the voltage applied between the gate and source of the drive transistor based on the acquired variation of the characteristic of the drive transistor.
Because this display device sequentially changes the offset voltage for a predetermined unit voltage, however, it takes a relatively long time to acquire an offset voltage corresponding to the variation of the characteristic of the drive transistor. The normal display operation cannot be carried out during acquisition of the offset voltage, it is not possible to frequently acquire the offset voltage.